The following discussion emphasizes the application of this invention to the design of loudspeaker systems. The system, however, is not limited in application to loudspeaker selection and positioning.
Loudspeaker systems may be classified into the two general categories of distributed systems and central systems. All other loudspeaker systems are variations on or combinations of the two. The central system locates a cluster or array of loudspeakers at one point, typically above the actual sound source. This system provides a greater sense of realism than the distributed system (absent use of sophisticated time delay devices), because the listener perceives the amplified sound as coming from the direction of the natural sound.
Design of a central system involves coverage of a given space with multiple loudspeaker units. Location and orientation, the angular and rotational placement of each loudspeaker, is important. Haphazard placement of component loudspeakers can result in excessively loud, low, or unintelligible sound in certain areas of the room. Since a loudspeaker system is a costly and significant item in a sound system, a way is needed to determine the best types of loudspeakers for the site, and the most effective way of orienting individual components with respect to a loudspeaker cluster and to the given room.
Many developments have been made in measurement techniques which describe the acoustical environment. By utilizing these developments, such factors as distortion, acoustical gain, and intelligibility can be measured and calculated relatively easily. But one of the most critical design factors of all, the orientation of the loudspeaker within a cluster, has lagged behind.
Descriptive-geometry drafting techniques have been used in the design of speaker systems, but such solutions cannot usually be obtained by showing the three principal views (front, top and side) which are used in orthographic projection. Many solutions require auxiliary views or revolution. This drawing process, as applied to the intersection of complex surfaces of an acoustical environment, and to the patterns of a source or receiver of sound, is very tedious to implement, time consuming and complicated. Furthermore, if the position of any element is to be moved, the entire process must be repeated for that component, and, in the course of designing, each cluster component may be moved several times before finding a correct orientation.
A projector which beams light through a template orifice to produce light patterns on a scale model has also been utilized, but only one loudspeaker coverage pattern at a time can be displayed, and loudspeaker interactions are not apparent. Another limitation is that the scale models take a significant amount of time to build. In addition, the model and the projector together are cumbersome to carry back and forth from office to site.
Recently, as an outgrowth of the increased information on sound coverage available, coupled with the advent of powerful programmable calculators and micro-computers, two-diminsional angular-mapping techniques have been devised. Their aim is to display the room as viewed from the loudspeaker cluster, to provide greater accuracy in component positioning, and in prediction of sound dispersion. The typical procedure is to measure the room, compute the data and make the necessary spherical to rectangular coordinate transformations, and to map the room on polar plot or graph paper. The commercially available speaker patterns --or the designer's own--are typically made of materials such as clear Mylar. These are shifted around over the room plot until the best coverage ascertainable from the method is achieved.
However, an axiom of cartography is that the only true map is a globe (a sphere). Transformations from a sphere to a flat two-dimensional surface attempt to minimize distortions as much as possible, but there is no such thing as a distortion-free flat map. If one attempts to flatten a sphere-like object (such as a child's rubber ball with surface designs) a clear idea of what happens in flat mapping can readily be seen. In any type of two-dimensional mapping, one or more of the following errors will occur. The scale of the map will be inaccurate, except along only one or two parallels or meridians, and angular relationships are not retained; or, relative sizes or shapes are distorted.
With two-dimensional mapping of loudspeaker clusters, the inevitable distortions cause the generated loudspeaker overlay to be accurate at only the area for which it is generated (and therefore inaccurate at all other positions), or require awkward and complex manipulations over the discontinuous two-dimensional map in order to see its true coverage pattern.
Accordingly a major object of this invention is to provide an improved means for designing a sound-system. Included within this broad purpose are the following specific objectives. With this invention, a sound system designer can "map" the entire listening area (including related architecture) onto a sphere without the distortion inherent in a two-dimensional transform of the same. Because overlays depicting the actual coverage of a loudspeaker can now be placed on this spherical map, and moved to any position or rotation with complete accuracy, it is possible to visualize immediately the loudspeaker's coverage anywhere.
The interaction of all loudspeaker components of a cluster can be readily seen. The attenuation contours of each loudspeaker can be compared to the inverse-square losses in the architectural surroundings to angle the loudspeaker into its optimum position, and to determine how much power is needed to deliver a desired direct sound pressure level. With available software, a system can be designed very rapidly, either in the field or in the office with equipment fitting into a standard attache case. The ultimate benefits of this technique expand beyond a more accurate sound system, to a more cost-effective sound system, and to a minimal-component sound system.